The disclosed subject matter relates generally to integrated circuit devices with sleep enabled power rails, and more particularly, a variable-width power gating module.
Secondary voltage rails are used in an integrated circuit device to selectively control the voltage supplied to one or more components of the device. For instance, an integrated circuit device may include one or more main power rails that provide power to the entire IC. The main power rail may be powered externally by either a battery or by a power supply directly connected to a power distribution service. When the device is turned on, power from the battery or the power supply connects to the integrated circuit device and charges the main power rail(s). Instead of connecting all of the integrated circuit device components to the main power rail, one or more components may be connected to a secondary voltage rail that is selectively switched on or off using a controllable switch.
This ability to selectively switch components on or off in an integrated circuit device is particularly important in handheld devices including, but not limited to, cell phones, personal digital assistants, portable entertainment systems, etc. In such devices, reducing the net power consumption of the device lengthens the amount of time between charges (or between replacements) of a battery power source. However, it is recognized that the selective ability to switch components on or off in an IC is also important to traditional computer systems that are not dependent upon a battery source. For instance, laptops are often designed to dissipate the least amount of heat so that the user is comfortable handling the system. It may further be valuable to reduce the net power consumed on a traditional computer system. It is further recognized that the physical size of an integrated circuit device and/or computer system, and the amount of operating noise associated with the device/system, may also decrease as the number and size of heat sinks and fans is reduced.
Conventionally, one or more switches in an integrated circuit device are used to selectively switch a voltage rail on or off, thereby selectively powering up or down components connected to the voltage rail. In this manner, the multiple voltage rails may serve to create voltage domains by dividing an integrated circuit device into voltage islands. In some integrated circuit devices, more than one voltage rail may be provided, thereby creating multiple voltage islands, each operating at the same or different voltage levels. One or more voltage rails may operate at a different voltage level than the main power rail.
In conventional circuits, transistors may be used to implement the one or more switches that power up a given secondary voltage rail. These transistors may be collectively referred to as a power gating module. The power gating module is responsive to a sleep (i.e., enable) signal for selectively powering or isolating the secondary rail. For example, the secondary rail may be isolated to place at least a portion of the integrated circuit device into a sleep mode. The sleep signal may be generated by any suitable device located on or off the integrated circuit device. In one example, a state machine may be used to enable or disable the sleep mode responsive to a determination that a specific voltage island is required to perform a given task. In the event a given voltage island is not required to work or perform the given task, the state machine enables the sleep signal (i.e., it puts the voltage island to sleep). In the event a given voltage island is required to function, the state machine disables the sleep signal (i.e., it wakes up or powers up the island). Such sleep control may be implemented in a highly dynamic manner.
Conventionally, the effective width, or current carrying capacity of the power gating module is fixed. In some implementations, a plurality of substantially identical transistors are concurrently enabled or disabled, resulting in a relatively large instantaneous current draw from the primary rail and the associated noise (e.g., voltage fluctuations and IR drops) when the secondary rail is powered. The large current draw may also cause possible electromigration (“EM”) violations due to the relatively large size of the PMOS transistors used in the power gating module. As known in the art, EM violations result when the current levels in a physical electronic connection are increased to the point where the connection physically breaks down and possibly burns. EM violations may occur from, for example, surpassing a maximum DC current, a maximum peak AC current, a maximum RMS AC current, etc.
To reduce the magnitude of the current fluctuation and to reduce the noise, a technique has been employed to stagger the enablement of the transistors in the power gating module using cascaded enable signals (i.e., the enable signal is delayed for some of the transistors). However, the overall width of the power gating module is not affected by the cascaded enable signal. Because, the power gating module effects the dynamic operation of the integrated circuit device, it has the potential to also affect the performance characteristics of the device, such as maximum frequency, minimum voltage, functionality (hold time), negative bias temperature instability degradation, high current conditions (contention/reset issues), interface timing, or other effects that may be attributed to a delta voltage on the supply. It is difficult for designers to gather information regarding whether the power gating module design is oversized or undersized. Hence, the sizing of the power gating module may negatively affect the performance grade of the device, and such degradation may be hard to quantify.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.